<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <script>
        var a = 10,b=11,c=12;
        function test(a){
            a = 1;
            var b = 2;
            c = 3;
        }
        test(10)
        console.log(a) // 10
        console.log(b) // 11
        console.log(c) //3
    </script>
</body>
</html>